September/October 2008: In This Issue

Forecast Center

by Tim Vasquez

Inspired by the famous Calvin & Hobbes cry of “Yukon ho!” Forecast Center follows the compass needle north to the taiga forests and tundra of the Arctic Circle. Though these regions are remembered for the cold winter blasts they bring to much of North America, the meteorological patterns in these territories are forgotten by many weather enthusiasts during the calm summer months. However, these months bring a heightened tempo of frontal passages, jet streams, and even showery weather. The rapidly changing weather keeps Canadian meteorologists on their toes at a time when much of the United States has fallen under the influence of upper-level ridging, the Bermuda high, and southwestern heat low.

This weather map is for an event during the mid-afternoon in July. Because pressure patterns are weak during the summer, draw isobars every 2 millibars, instead of the normal 4 (1004, 1002, 1000, 998, 996, etc.), using the plot model example on the side as a guide. As the plot model indicates, the actual millibar value for plotted pressure (xxx) is 10xx.x mb when the number shown is below 500, and 9xx.x when it is more than 500. For example, 027 represents 1002.7 mb, and 892 represents 989.2 mb. Therefore, when one station reports 074 and a nearby one shows 086, the 1008 mb isobar will be found halfway between the stations. Then try to find the locations of fronts, highs, and lows..

TIM VASQUEZ is a former Air Force forecaster and author of Digital Atmosphere, a weather-forecasting software program. He lives near Austin, Texas, where he keeps busy as a weather consultant and software developer.